This invention relates to apparatus and methods for separating particulate matter (solid particles and/or liquid droplets) from a fluid stream.
It is often desirable to remove particulate matter from a fluid stream. For example, it may be desired to simply cleanse the fluid of the particulate matter, or at least reduce the concentration of the particulate matter in the stream. In other instances, the goal is to capture a certain size range of particulate matter for analysis and/or characterization. Sometimes, the aim is to simply concentrate the particulate matter so that it can be used in some way.
A large number of devices exist for this purpose. These include various types of filters, cyclones, electrostatic precipitators, among other devices. For removing very small particulate matter, such as aerosol particles and microorganisms, from a gas stream, various types of virtual cyclones and virtual impactor devices have been devised. Examples of these are described in U.S. Pat. Nos. 6,156,212 and 6,386,015 (micromachined virtual impactor), U.S. Pat. No. 6,432,630 (micro-flow system using an external field to deflect particles), U.S. Pat. No. 6,270,558, U.S. Pat. No. 6,465,225 (centrifugal- or gravity-fed deflection system); U.S. Pat. No. 6,467,630 (column with applied “convective force”); and U.S. Pat. No. 6,062,392 (virtual impactor).
In many applications, it is necessary to perform the separation of particulate matter using small, lightweight apparatus that operates simply and requires minimal energy. In many devices, an efficient separation can be performed only if there is a high pressure drop through the device, or if some other energy (such as to create an external, particle-deflecting field) is applied. To address this problem, U.S. Pat. No. 6,110,247 describes a micropillar device which relies on an array of micropillar rows to capture particles from a fluid stream. The micropillar device provides separation of particulate matter at moderate pressure drops, while still allowing for recovery of the captured particulate matter.
However, it is desirable to obtain further improvements in separation efficiency. In particular, it is desirable to operate under lower pressure drops than exhibited with the micropillar device of U.S. Pat. No. 6,110,247. In addition particle capture efficiency with such micropillar devices is often less than desirable, because particles tend to bounce off of micropillar surfaces (in part due to high impact velocities). Thus, particles colliding with the micropillar surfaces tend often are able to nonetheless pass through the device and avoid collection.